How much difference to performance do scratches and marks on a front wing make in terms of real world use?

Let's assume that the shape and structure of the wing is fully intact but there are scratches and fine marks along the front and face of the wing. How much difference does it make to performance?

I saw a recent Blue Planet video and Robert and the guys he was riding with had front foils that looked liked they had been scraped and hacked on the coral and rocks more than once. Didn't seem to affect their wave riding too much.
I'm sure if you're racing and chasing seconds, it could be a consideration.

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MilesH said..
How much difference to performance do scratches and marks on a front wing make in terms of real world use?

Let's assume that the shape and structure of the wing is fully intact but there are scratches and fine marks along the front and face of the wing. How much difference does it make to performance?

No difference for average punter. Racer possibly due to ventilation issues.

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kersh said..
I saw a recent Blue Planet video and Robert and the guys he was riding with had front foils that looked liked they had been scraped and hacked on the coral and rocks more than once. Didn't seem to affect their wave riding too much.
I'm sure if you're racing and chasing seconds, it could be a consideration.

I saw a blue planet with one of the wing designers, can't remember which one but he said they have a huge affect on performance and recommend filling and sanding them smooth.

Noticable even on slow foils. Rough, greasy foils will stall earlier. You can still foil a banged up greasy foil but I definitely notice an improvement in bottom end after I've filled and sanded mine. Start with 400 then 600, 800 and finish with1000 -1200.

Keeping them clean helps too, I give mine a wipe down with Windex if they get greasy

Unless you are into racing, sanding foils to perfection perhaps has some positive effect for an average rider but only as a placebo. Whatever makes us feel more comfortable or happy - it is all good.

Noticed a difference between matte finish and gloss on old SAB foils. Especially if you sand one side and not the other

Sanding a foil to a race finish really helps and not just for the racers. Those of us chasing swell or waves will really notice a sanded and cleaned foil. Snap turns at high speed are possible without that horrible ventilation that can occur when using a waxy or dirty foils. The foil seems to grip the water as you lay the board over and makes for a very pleasant ride.
All my foils are cleaned with windex prior to hitting the water.

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Foilmate said..
Noticed a difference between matte finish and gloss on old SAB foils. Especially if you sand one side and not the other

Foilmate Could you elaborate some on these effects one side sanded the other gloss?

I assume you sanded the top side for water to move faster on top for more lift...

OP, I think it was Ken Wieners who said scratches make a big difference.
I bought a used very scratched foil, it definitely felt like it performed better after I cleaned it up.

I also had a aluminium mast that comes new with a rough textured surface. It wasn't hard to get it to ventilate. Painted and sanded it and it's never ventilated sense.

I was told by a naval architect that you don't need to sand much finer than 320 grit - even 600 was overkill(...something about the thickness of boundary layer...) so I have always finished with linear passes of 400... seems to make a difference vs scratched up foil but I doubt you will notice sanding to 2000 grit...

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gorgesailor said..
I was told by a naval architect that you don't need to sand much finer than 320 grit - even 600 was overkill(...something about the thickness of boundary layer...) so I have always finished with linear passes of 400... seems to make a difference vs scratched up foil but I doubt you will notice sanding to 2000 grit...

And... 400 to 600 is faster than 1000+!

It has been shown in test tanks by naval architects since at least the forties.

A test to see if you must sand: Hose your hull / foil: the water should flow in sheets, not form droplets.

Another test: your hand flat on the hull and try to slide it: it will stick on a glossy surface, but slide as on bearing balls on a 400-sanded one.

See: boardlady.com/fast.htm

Was weird going up from 1200 to1500 grit on my 550 foil, actually felt like it was harder to get up on foil. Was back to back sessions on exactly same gear and very similar conditions. Once up it was hard to tell any difference. I'd done the same with my 700 foil and it felt a little harder to get going too.

Could have all been in my head or something about the conditions that changed slightly.

Huge difference when you put first scratch on new foil ... after that no difference at all. ;-)

What is the best way to go about doing this ? I've seen recommendations for either epoxy or PU prior to sanding ? any tutorial you'd recommend ?

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gorgesailor said..
I was told by a naval architect that you don't need to sand much finer than 320 grit - even 600 was overkill(...something about the thickness of boundary layer...) so I have always finished with linear passes of 400... seems to make a difference vs scratched up foil but I doubt you will notice sanding to 2000 grit...

There was a chart that showed optimum sand paper grit should be based on desired speed... And if I remember correctly 320 grit was good for the 20 or 25 knotts.

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chawalman said..
What is the best way to go about doing this ? I've seen recommendations for either epoxy or PU prior to sanding ? any tutorial you'd recommend ?

No need to epoxi light scratches. It will be too much work sanding and may affect the wing profile if not sanded correctly.
I have been using bondo putty on all my foils and mast to cover fine marks and is very straightforward and easy to sand only with fine sandpaper:
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I accidently foiled onto a slab of concrete and really tore up the bottom so, I tried the super glue and baking soda fill. Wow, I was impressed how quick and easy it was to repair. Give it a try sometime.

Stratches on the leading edge can cause flow separation issues. The boundary layer is thinnest at the leading edge so important to have it fair and smooth.

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windwakerider said..
I accidently foiled onto a slab of concrete and really tore up the bottom so, I tried the super glue and baking soda fill. Wow, I was impressed how quick and easy it was to repair. Give it a try sometime.

Try superglue + powdered graphite. Same colour as the carbon foil and slightly softer to sand.

The 'surface finish' has been a topic I have followed for 40years. K1 Olympic kayaks polish to as high a floss as possible, as do racing powerboat s. I once met the Italian K4 team and watched them polish their kayak with a paste that was app 10k grit. Was told it was what the military used to polish the canopies on fighter jets to get the most perfect finish. I am no expert but I sand my foils to 2000 grit, then polish with paste and electric buffer to a mirror finish. Feels slick. but maybe just placebo effect.

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kersh said..
I saw a recent Blue Planet video and Robert and the guys he was riding with had front foils that looked liked they had been scraped and hacked on the coral and rocks more than once. Didn't seem to affect their wave riding too much.
I'm sure if you're racing and chasing seconds, it could be a consideration.

It was after watching that video I stopped worrying about my front foil. Theirs were very beaten up but man were they graceful riding them!